Radiation transfer in fibrous media with large size parameters

Radiation transfer in fibrous media with large size parameters has been numerically investigatad using a pseudo-continuous model. In this study, first, we examine how the scattering from a single fiber can be approximated by the specular reflection on the fiber surface and the Fraunhofer diffraction of a rectangular aperture which is considered to be a single fiber. Considering the Fraunhofer diffraction and specular reflection, we derive approximate solutions for estimating the optical characteristics of fibers, such as extinction and scattering efficiencies, which are required in this model. By comparing the approximate solutions with the conventional exact solutions, it is shown that the approximate solutions are useful at size parameters of more than 50 and at absorption indexes of more than 0.1. Furthermore, with use of the optical characteristics obtained by the approximate solutions in combination with the conventional exact solutions, radiation transfer in two types of planar fibrous media with typical fiber orientations is estimated, and the effects of the optical constant of fibers, fiber diameter and the orientation on the radiation transfer in the media are presented.